This will unlock an instruction manual to transform the batmobile to the batblaster. Follow the instructions (or not ) and SAVE to the toy tag! Once it's done, achievement should pop.

(I didn't follow the instructions in real world because the LEGO Batmobile has a better look than the BatBlaster. But I've saved it to the toytag and when I put the toytag on the pad, my Batmobile is the batblaster on screen).

If you just buy the batblaster model without saving it to the toy tag, achievement will not pop.

If you didn't and leave the upgrade screen, no worry : go back to the upgrade screen and you can build the batblaster to have the opportunity to save the batblaster to the toytag without spending again the 10 000 studs and the 3 gold bricks.